Known production fish hatcheries represent a large capital investment. They have stationary locations and include costly high-volume pumps, large filtering systems, water heaters, large tanks and a variety of accessory equipment. All of these items are ordinarily housed in one or more buildings. In addition, known fish hatcheries use relatively large quantities of water. It is common for a hatchery to use 600 volumes of water per volume of eggs per day. For example, in a conventional walleye hatchery, it is not uncommon to circulate more than one million gallons of water through 500 quarts of eggs during a fifteen day incubation period. A similar volume of coregonid eggs incubated for a hundred and fifty days uses more than ten million gallons of water. Thus, even though hatcheries are often operated only a few weeks each year, the massive equipment must be permanently housed in special buildings, and the buildings must be restricted to sites having an adequate source of suitable surface or ground water.
Laboratory hatching systems are in stark contrast to the presently known production hatcheries. These systems tend to be small and are utilized to incubate only small quantities of eggs. An example of this type of system uses a twenty liter, insulated bucket to maintain subunit containers in a common, temperature-controlled water bath. Compressed air, distributed by an air stone, transports oxygenated water from a biological gravel filter up a narrow pipe. The overflowing water causes the water level to rise in a surrounding pressure tube. The resulting overpressure forces the oxygenated water to pass through connection tubes from the pressure tube to the walls of the subunit containers. Water from the subunit containers returns to the gravel filter for recirculation. The subunit containers are typically on the order of 7 centimeters in diameter and 1 centimeter high. During incubation, dead eggs are removed from the system using a pipette. Water is recirculated as described and exchanged approximately every thirty minutes. The system is sufficiently small that a number of samples using different water salinities or other varying parameters may be tested efficiently.
Prior to the present invention, it has not been possible to use laboratory type systems on a production scale. Thus, there has been a distinct need for an inexpensive, portable, production incubation system.